When Macintosh computers (e.g. iMacs) are shipped from the factory, they have a standard set of system software (e.g. Mac OS 9.1) installed on them.

Subsequent to that time, Apple issues updates to many of the components of this standard package. In almost all cases, these incremental updates are available for free.
{These updates are easily — or automatically, with the Software Update Control Panel — downloadable from Apple, or manually downloaded through Mac software
sites (e.g. VersionTracker).}

The reasons of these updates are: 1) to improve performance, and/or 2) to add features, and/or 3) to correct errors.
The benefits of utilizing these free updates are often substantial.

Below are some notable (i.e. where Hardware, or System Extensions are modified) iMac and 9.1 updates (all free). Although using all these updates is usually beneficial,
the bold items below are the most important ones.

The bottom line is that any iMac or OS 9.1 Mac that is not using most of these free updates, will definitely
be more prone to conflicts, and will have poorer performance.

[Note: 9.1 is a very dependable version, and is the minimum OS that should be used where possible. It can be installed on any Macintosh that originally shipped with a PowerPC processor
that has at least 32 megabytes of physical RAM (more RAM is very beneficial). See for more info from Apple.]